The present invention relates to a pile foundation structure for supporting a footing serving as a foundation of a large-scaled and heavy upper structure such as a high building, and propagating a load of the upper structure to the underground depths by means of plural point bearing piles or friction piles disposed within a construction range of the upper structure so as to be spaced from each other, and driven into the undergrounds such as a solid rock.
Such a pile foundation structure is conventionally known, such as the structure illustrated in FIGS. 11 and 12. In other words, it has a structure wherein plural point piles or friction piles 100 (hereinafter called piles) disposed within a construction range (shown by the outline thereof) of an upper structure A so as to be spaced from each other, is driven into the underground B, such as solid rock, and a head of the each pile 100 i.e., a pile head is buried into a foundation 101 (hereinafter called a footing) on a side of the upper structure A, whereby the pile 100 is rigidly joined to the footing 101.
FIG. 13 illustrates in detail a joint structure between each pile 100 as a structure element and the footing 101. A lower end ofthe footing 101 is mounted on a head of the pile 100, and the pile 100 is rigidly jointed to the footing 101 by reinforcing steel members 102 including a pile reinforcement and a concrete-reinforcing bar, and concrete.
As mentioned above, the conventional pile foundation structure is constructed so that each pile foundation has the pile 100 rigidly joined to the footing 101 so that it is longitudinally and laterally disposed within the construction range ofthe upper structure A, so as to be appropriately spaced from each other. In case of the conventional pile foundation structure, earthquake motion which is propagated from the underground B when an earthquake happens, is input to the upper structure A via a rigid joint portion between the head ofthe pile 100 and the footing 101. In this moment, it is not only that a stress such as a shear force is concentrated on the joint portion of the head of each pile as a boundary portion between both of them, but also that, even if joint between heads of the piles 100 and the footing 101 is perfect, a great bending moment happens on the pile 100 in the underground B. As a result, the joint portion between the pile head and the footing 101, and the pile 100 are easily damaged and destroyed. Thus, it is extremely difficult and requires a long period and huge costs to conduct a restoration construction in case that damage or destruction is caused on the pile 100, and the joint portion between the pile head and the footing 101.
In order to resolve the above problems, the pile foundation structure employing a sliding structure is suggested in a gazette of published Japanese Patent Application Laying-Open No. 1-102124.
In other words, the pile foundation structure shown in FIG. 14 is structurally described below. A number of steel reinforcement members 103 annularly disposed on an upper end of the pile 100, and steel pipes 104 disposed so as to surround the steel reinforcement members 103 in a state of allowing lateral movement of the steel reinforcement members 103 are upwardly extended. At each lower end portion of the steel pipes 104, annular engagement projections 105 are arranged so as to be connected to an upper end portion of the pile 100 in a buried state. Moreover, a top board 106 is welded to the upper end portion of the steel pipes 104, the top board 106 is provided with flexible holes 107 for making the steel reinforcement members 103 pierce the top board 106 so as to respectively allow lateral shaking of the steel reinforcement members 103. The steel reinforcement members 103 protruding above the top board 106 through the flexible holes 107, are connected to the footing 101 of the upper portion thereof. Furthermore, there is a sliding member 109 between the top board 106 and a footing metal member 108, through which the footing 101 is slidably mounted on the top board 106.
In the pile foundation structure having such a sliding arrangement, when the earthquake motion is applied, the steel reinforcement members 103 are bent, and at the moment while they are bent, the sliding member 109 makes the footing 101 slidingly move with respect to the pile 100, thereby making it possible to restrict stress concentration on the joint portion of the pile head. However, the sliding amount is regulated by the size of each flexible hole 107 disposed on the top board 106, and the pile 100 is connected to the footing 101 by the steel reinforcement members 103 whereby the shearing force and the bending moment cannot be efficiently absorbed in case of applying the excess earthquake motion. Consequently, it is unavoidable that the joint portion between the head ofthe pile 100 and the footing 101 is damaged or destroyed. In the same way as the conventional pile foundation structure in FIG. 13, there has been a problem wherein earthquake-proof property and earthquake avoidable property cannot be ensured enough.
The present invention has been conducted in view of the above mentioned circumstances, i.e., the background of the prior art. Objects of the present invention are to provide a pile foundation structure which can reduce stress concentration applied to a joint portion of a pile head and a bending moment applied to the pile which are accompanied with earthquake motion; make a whole of a structure lightweight; reduce costs; prevent the pile and the joint portion of the pile head from being damaged or destroyed; and also enhance excellent positional restoration performance of an upper structure after the earthquake happens.
A first aspect of the invention relates to a pile foundation structure for joining a footing of an upper structure to heads of plural piles (or pile heads) disposed within a construction range of the upper structure so as to be spaced from each other, and driven into the underground, characterized in that
a roller bearing structure is constructed as each joint structure between some of the plural piles and portions of the footing of the upper structure corresponding thereto, wherein
a protrusive-supporting-portion having a flat top surface is disposed on a side of the pile head, in a state of protruding above an upper surface of the underground,
a recessed-joint-portion having a flat top surface is disposed on a side of the footing of the upper structure, so as to correspond to the protrusive-supporting-portion and be greater than the protrusive-supporting-portion, and
a sliding member is interposed between the top surfaces of the protrusive-supporting-portion and the recessed-jointing-portion,
thereby making it possible to relatively slidingly move a joint portion of the head of the pile in a horizontal direction; and
a pin bearing structure is constructed as each joint structure between the others of the plural piles and portions of the footing of the upper structure corresponding thereto, wherein
a spherical-supporting-portion having a convex or concave outer surface is disposed on a side of the pile head, in a state of protruding above the upper surface of the underground,
a spherical-joint-portion having a concave or convex inner surface is disposed on a side of the footing of the upper structure, so as to correspond to the spherical-supporting-portion and be greater than the spherical-supporting-portion, and
a sliding member is interposed between the outer surface of the spherical-supporting-portion and the inner surface of the spherical-joint-portion of the footing of the upper structure,
thereby making it possible to relatively slidingly rotate the joint portion of the head of the pile.
According to the first aspect of the present invention having such an arrangement, the earthquake motion which is propagated from the underground when the earthquake happens, is input to the upper structure via the each supporting portion of the roller bearing structure and the pin bearing structure in each head of the plural piles. In this time, a horizontal component of the earthquake motion is mainly absorbed by a sliding effect of the roller bearing structure wherein the protrusive-supporting-portion is disposed on a side of the pile head, and the recessed-jointing-portion is disposed on a side of the footing, and the sliding member is interposed between the flat top surfaces of the protrusive-supporting-portion and the recessed-jointing-portion, which are opposed to each other. This makes it possible to decrease the stress concentration applied to the joint portion of the pile head and a bending moment which occurs on the pile driven into the underground. On the other hand, though the upper structure is easily rotated when a great external force such as the earthquake motion is applied to the upper structure, the rotation of the upper structure can be restrained by means of the pin bearing structure wherein the spherical-supporting-portion is disposed on the pile head, the spherical-jointing-portion is disposed on the footing, so as to correspond thereto, and the sliding member is interposed between the outer surface of the spherical-supporting-portion and the inner surface of spherical-jointing-portion. Moreover, the pin bearing structure can ensure the positional restoration performance of the upper structure after the earthquake happens.
As mentioned above, the joint portion between the each head of the plural piles and the footing of the upper structure is built as a complex structure of the roller bearing structure which is excellent in the absorbing property of absorbing horizontal shakes, and the pin bearing structure which is excellent in the absorbing property of absorbing vertical shakes, and rotation restraint property. This structure can prevent the pile itself and the joint portion of the pile head from being damaged and destroyed, thereby making it possible to decrease an amount of an arrangement of reinforcement used for the pile and footing, make a whole of the structure lightweight, reduce costs, and exhibit the excellent earthquake avoidable property.
In case of employing the pile foundation structure having such a complex structure, especially, the structure which includes the roller bearing structure disposed within the construction range of the upper structure, and the pin bearing structure disposed on an outer periphery of the roller bearing structure, the external force such as the earthquake motion is applied thereto, with the result that the pin bearing structure restrains the horizontal movement of the upper structure on a side of the outer periphery of the roller bearing structure whose amount of the horizontal movement is greater than that of the portion supported by the roller bearing structure, which allows horizontal sliding movement of the upper structure. This can further improve the positional restoration performance of the upper structure after the earthquake happens.
A second invention of the present application relates to a pile foundation structure for jointing a footing of an upper structure to heads of plural piles disposed within a construction range of the upper structure so as to be spaced each other, and driven into the underground, characterized in that
a rigid joint structure employing reinforcing steel material and concrete is constructed as each joint structure between some of the plural piles and portions of the footing of the upper structure corresponding thereto; and
a roller bearing structure is constructed as each joint structure between the others of the plural piles and portions of the footing corresponding thereto, wherein
a protrusive-supporting-portion having a flat top surface is disposed on a side of the pile head, in a state of protruding above an upper surface of the underground,
a recessed-jointing-portion having a flat top surface is disposed on a side of the footing of the upper structure, so as to correspond to the protrusive-supporting-portion and be greater than the protrusive-supporting-portion, and
a sliding member is interposed between the top surfaces of the protrusive-supporting-portion and the recessed-jointing-portion,
thereby making it possible to relatively slidingly move a joint portion of the head of the pile in a horizontal direction.
Accordingly, in the second embodiment having such a structure, in case that the external force such as the earthquake motion propagated from the underground is applied to the upper structure when the earthquake happens, the rigid joint structure between the pile head and the footing controls the rotation of the upper structure. Moreover, when the great horizontal component accompanied with the earthquake motion or the like is applied thereto, the horizontal component is absorbed by means of the sliding effect of the roller bearing structure, thereby making it possible to decrease the stress concentration applied to the joint portion of the pile head and the bending moment occurring on the pile. As a result, when the great external force such as the earthquake motion is applied thereto, it is possible to prevent the joint portion of the pile head and the pile itself from being damaged and destroyed, and to exhibit the excellent earthquake avoidable property.
The pile foundation structure according to such a complex structure including the rigid joint structure and the roller bearing structure, may have either an arrangement wherein the roller bearing structure is disposed within the construction range of the upper structure, and the rigid joint structure is disposed on a side of the outer periphery of the roller bearing structure, or an arrangement wherein the roller bearing structure is disposed within the construction range of the upper structure, and the rigid joint structure is disposed on a side of the inner periphery of the roller bearing structure. However, the former arrangement is more preferable. Namely, in case of the former arrangement, the external force such as the earthquake motion is applied thereto, with the result that the rigid joint structure restrains the horizontal movement of the upper structure on a side of the outer periphery of the roller bearing structure whose amount of the horizontal movement is greater than that of the portion supported by the roller bearing structure, which allows horizontal sliding movement of the upper structure. This can prevent livability from worsening owing to unnecessary rocking of the upper structure, even if relatively small external forces such as a traffic vibration and a wind load are usually applied thereto. Moreover, when the great external force such as the earthquake motion is applied thereto, this can further exhibit the damage and destroy prevention functions for preventing the pile and the joint portion of the pile head from being damaged and destroyed.
A third invention of the present application relates to a pile foundation structure for jointing a footing of an upper structure to heads of plural piles disposed within a construction range of the upper structure so as to be spaced each other, and driven into the underground, characterized in that
a rigid joint structure employing reinforcing steel material and concrete is constructed as each joint structure between a pile disposed on a side of the center of the construction range of the upper structure, among the plural piles, and a portion of the footing corresponding thereto; and
a pin bearing structure is constructed as each joint structure between piles disposed on the outer periphery of the construction range of the upper structure and the footing of the upper structure, wherein
a spherical-supporting-portion having a convex or concave outer surface is disposed on a side of the pile head, in a state of protruding above the upper surface of the underground,
a spherical-jointing-portion having a concave or convex inner surface is disposed on a side of the footing of the upper structure, so as to correspond to the spherical-supporting-portion and be greater than the spherical-supporting-portion, and
a sliding member is interposed between the outer surface of the spherical-supporting-portion and the inner surface of the spherical-jointing-portion of the footing of the upper structure,
thereby making it possible to relatively slidingly rotate a joint portion of the head of the pile.
In the third embodiment having such an arrangement, in case that the external force such as the earthquake motion propagated from the underground is applied to the upper structure when the earthquake happens, the rigid joint structure between the pile head and the footing restrains the upper structure from rotating. When the external force which is above the predetermined value is applied thereto by the earthquake motion or the like, the stress is released by sliding rotation of the pin bearing structure, thereby making it possible to decrease the stress concentration applied to the joint portion of the pile head and the bending moment occurring on the pile. This can prevent the joint portion of the pile head and the pile itself from being damaged and destroyed. Moreover, the underground is horizontally moved, there by moving the center of the gravity of the upper structure. As a result, deformation occurs on the pile in which the rigid joint structure is adopted, and vertical motion of the upper structure occurs according to the rotation of the pile head, which is built as the pin bearing structure. Consequently, the structure can ensure the positional restoration performance of the upper structure after the earthquake happens.
In the each pile foundation structure according to the first to third inventions having the above structures, a caulking compound is structurally enclosed with a sliding surface between the supporting-portion of the pile head and the jointing-portion of the footing. The caulking compound enclosed with the sliding surface between the supporting-portion of the pile head and the jointing-portion of the footing can enhance the vibration absorption property, and prevent water from intruding from the outside to the sliding surface. Accordingly, corrosion of a steel material as a structural element is decreased, and deterioration of the sliding member is decreased, thereby keeping sliding movement and sliding rotation properties caused by the sliding member smooth and stable for a long period as effects thereof.
Furthermore, the each pile foundation structure according to the first to third inventions has an arrangement wherein metal parts made of metal are respectively closely fitted into the outer surface of the supporting-portion of the head of the each pile and the inner surface of the jointing-portion of the footing, and the metal parts are integrally connected to the head of the pile and the bottom of the footing via anchor members. Then, the arrangement can have the effects of surely preventing damage and destroy of the pile head and the footing, and keeping predetermined sliding movement and sliding rotation properties smooth and stable.
In addition, according to the each pile foundation structure according to the first to third inventions having the above structures, a material having self-lubricative property is employed as the sliding member. Therefore, even in case that this is the first time that the structure, wherein a long time passed since the execution of the structure, has undergone the external force such as the earthquake, the predetermined sliding movement and sliding rotation properties are ensured.